Tap stud or the like



place when the nut or 12, herein also a straight me srun on was man .iohn L. Cook, Wrentham, mesne assignments, to Qompany, Wrentham, Mass.,

P ssachusetts Mass., assignor, by Wrentham Products a corporation of Application September '1, 1940, Serial No. 355,724

2 Claims.

This invention relates to studs or like devices for screw-threaded anchorage in a metal body to project thereirom, usually to secure some other device, as by means of a nut on the projecting end thereof, and the object is to provide a device of this nature which may be screwed directly into a hole of suitable size and which will by such action be firmly anchored therein.

The present practice in installing studs is to provide holes of suitable size in the body upon which they are to be mounted, which holes are then tapped to receive a thread on the stud which is screwed in. Since the studs are more or less a permanent fixture the like on the projecting end is removed, a wrench-tight fit is desired. In accordance with my invention I provide a device which dispenses with the separate tapping operation and insures a tight engagement with the threaded connection.

My invention will be'well understood by reference to the following description taken in connection with the accompanying drawing, where- Fig. l is a side elevation of a stud illustrative of the invention, a portion of the metal body in which it is mounted being shown in section;

Fig. 2 is an end view of the same as shown from the rightof Fig. 2; and

Fig. 3 is a section on the line 3-3 of Fig. 1 on an enlarged scale.

Referring to the drawing, the stud there shown comprises a cylindrical metal body 6 having a thread 3 at the outer end, the left-hand end of Fig. 1, to receive a nut. The thread at the other end serves for fixing the stud to the body or metal it on which it is to be mounted and it comprises an outer thread-cutting portion l2 merging into an inner threaded portion 14 which primarily provides the screw threaded anchorage for the stu The thread it has sloping flanks as shown and may be of any usual or desired profile and of appropriate pitch, such as that standard or suitable for the body diameter in question, and it merges, it being of the usual straight or cylindrical type as contrasted with a taper thread, as best shown in Fig. 3, into the cutting thread thread, which is of the same cross-sectional profile and pitch but of a lesser pitch diameter, as hereinafter more fully explained. The thread 12 is tapered off as illustrated and provided with flutes it in the manher of a tap. As indicated in Fig. 2'by the eccentric full lines adjacent the concentric dotted line,

designed to remain in the outer surface portions of the cutting thread between flutes it are eccentrically relieved at their region behind their leading or cutting edge, that is, circumferentially, in the direction of entering rotation of the stud. At least a portion of the stud comprising the thread 52 is suitably hardened so as to be able to cut the metal l0, and as the device is designed for a single use case hardening is efiective.

To'utilize the stud the work it is provided with an opening it of a diameter at least equal to the root diameter of the thread it. Ordinarily the diameter would be somewhat greater. the line a-a indicates the normal position of the wall ofthe hole relative to the stud when the latter is in place and is seen to iall somewhat beyond the root diameter of the thread it, thus providing about an thread. The line b-b indicates the pitch diameter of the thread i2, that is, the diameter half-way between the crest and the root of a theoretical; completely sharp v thread of the contour in question, and, in the case of a United States Standard form of thread, half-way between the actual major and minor diameters, this diameter being the measure of the effective size of a thread because the surface of contact between a screw and a threaded hole lies at the thread flanks rather than at the crest of the thread. The line 0-0 similarly indicates the pitch diameter of the thread ii and it will be seen that the latter is slightly greater than that of the thread E2, the difference it being about .003 of an inch in a thread of ordinary size. It will be noted in Fig. 3 that the same differential exists between the root diameters of the threads illustrated, but i have indicated the pitch diameters because these are the really important measurements. The outside diameters and the root diameters are not important as the tight fit is wanted at the sides of the thread.

Referring to Fig. 3 and considering a normal crosssection Mia oi the thread it and a similar normal cross-section i201, of the thread l2, it will be seen that these are identical in form but offset relatively tothe axis of the stud, the'position Ma corresponding to a displacement upwardly in the figure or radially, considering the cylindrical body, from the position 82a. Hence if the thread It enters into a female thread cut by the thread H, the action is as if iEa were pressed radially outward into a corresponding groove, wedging into the taper oi the thread, the flanks oi the male thread pressing outwardly against the flanks of the female thread and insuring tight engagement.

In Fi 3 III, which is the usual position desired. The

thread ll will enter the female thread which I has been cut and very flrmly engage the same against any possibility of accidental loosening therefrom by virtue of the wedging action Just described. As is apparent from Fig. 3, in the .form of the invention shown the outside diameter of the thread It is a little greater than the outside diameter-of the thread l2, but thedifferential in question being slight, this does not prevent the thread H from being screwed in. Alternatively, if desired, the thread H might be made with wider flats, that is, with a smaller exterior diameter, provided the general profile remains the same as that of the thread I! and the pitch diameters show the differentiation Just described and indicated in Fig. 3 by the spacing d between the lines 17-1) and -0.

I am aware that it has been proposed to provide bolts with an ordinary machine thread of uniform pitch diameter and to cut flutes in their ends so that the end portions would cut in the manner of a tap, but without relief of the interflute portions of the thread and such constructions would not provide for the tight anchorage desired in a stud or similar device and herein efiected by the step or differentiation between the pitch diameters of the cutting and retaining threads.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

I claim:

1. A device for securing anchorage to metal comprising a cylindrical body having at its end a straight thread intersected by one or more cutting flutes, the distal portion of the thread being tapered off and the proximal portion being complete in cross section, said thread constituting an instrumentallty for cutting a straight female thread, the body having also inwardly of said thread and extending therefrom a straight retaining thread of the same form and pitch as the flrst mentioned thread but having a pitch diameter slightly greater whereby it will screw into the female thread cut by the cutting thread with an outward wedging action between the opposed thread flanks throughout the major surface area thereof.

2. A device for securing anchorage in metal comprising a body having a thread at the end thereof intersected by one or more cutting flutes, the distal portion of the thread presenting an external taper toward the end and the proximal portion being a straight thread of complete cross sectional form, the thread as a whole constituting an instrumentality for cutting a straight female thread corresponding to the straight proximal portion, the body also having inwardly of said'straight thread and extending therefrom a straight retaining thread of the same form and pitch as the first mentioned straight thread but having a pitch diameter slightly greater whereby it will screw into the female thread cut by the cutting thread with an outward wedging action between the opposed thread flanks throughout the major surface area thereof.

' JOHN L. COOK. 

